1. Field of the Invention
The present invention relates to a planetary differential assembly used in a power train of a vehicle.
2. Description of the Prior Art
Heretofore, it is well known to provide a conventional differential assembly using a planetary gear system, which assembly has a construction in which, for example: an internal gear is fixedly mounted on both of a driven gear and a differential case; a sun gear is coaxially arranged with the internal gear while rotatably arranged with respect to the differential case; a first planet gear is meshed with the internal gear; a second planet gear is meshed with the first planet gear while meshed with the sun gear; a planet-gear carrier for rotatably carrying the first and the second planet gear is rotatably arranged with respect to the differential case; the sun gear is connected with one of axle drive shafts, for example such as a left-hand axle drive shaft; and the planet-gear carrier is connected with the other of the axle drive shafts, i.e., a right-hand axle drive shaft.
In the conventional differential assembly having the above construction, when torque is transmitted to the differential case through the driven gear, the internal gear (which is integrally formed with the differential case) is rotatably driven so that the torque is further transmitted to both the sun gear and the planet-gear carrier through the first and the second planet gear, whereby the left-hand axle drive shaft (which is connected with the sun gear) is rotatably driven together with the right-hand axle drive shaft which is connected with the planet-gear carrier.
However, in some cases, for example, in case that the left-hand driving wheel of the vehicle loses traction due to a bad ground condition in traveling, then the other or right-hand driving wheel of the vehicle cannot deliver torque. In order to prevent this undesirable phenomenon from occurring in traveling, in other conventional differential assemblies (which is used in the vehicle) such as those disclosed in documents or Japanese Patent Laid-Open No. 61-96238 (called in Japanese language, Tokkaisho 61-96238) and Japanese Utility Model Laid-Open No. Hei 1-166157 (called in Japanese language, Jikkaihei 1-166157), the internal gear is limited in rotation relative to the planet-gear carrier or relative to the sun gear, so that relative rotation between: the left-hand driving wheel connected with the sun gear; and the right-hand driving wheel connected with the planet-gear carrier is limited to enable the driving wheel (which still keeps traction) to deliver torque.
However, as is clear from drawings attached to each of the above documents, in order to limit the relative rotation between the internal gear and the planet-gear carrier or that between the internal gear and the sun gear, it is necessary for each of the conventional differential assemblies to provide a multiple-disk clutch and like mechanisms therein. However, such multiple-disk clutch and like mechanisms make each of the conventional differential assemblies complex in construction and require much space, which necessarily enlarges each of the conventional differential assemblies in size. In addition, each of the conventional differential assemblies suffers from noise in operation unless it uses special lubricating oils. These are problems inherent in the conventional differential assemblies used in the vehicles.